1. Field of the Invention
The present invention relates to a tape guide for an arcuately scanning tape drive and more particularly to a tape guide which has a sloping surface in close proximity to a rotating head assembly for equalizing tension per unit width across the tape as the tape makes transducing contact with magnetic heads on the head assembly.
2. Description of Related Art
The most commonly-used direct access storage device in portable and desktop computer systems is the Winchester disk of three and one-half inches or less. The three and one-half inch Winchester disk has a capacity of storing in excess of 40 megabytes of data. Prudent computer system management requires that the data on a Winchester disk be periodically copied (backed-up) so that it will not be lost in the event of a head crash. Further, it may be desirable to preserve Winchester-stored data in an archive or library or in a medium which can be manually transported to another computer system. Also, security requirements may necessitate erasing a disk and/or storage of transportable media in secure locations. Magnetic tape is widely used for these purposes.
Most commercially important magnetic tape drive systems are based on the reel-to-reel transport of magnetic tape past a fixed recording/reading location where a stationary single- or multiple-track head is positioned. Recording and playback in such a system is done longitudinally with respect to the tape by moving the tape on its longitudinal axis past a record/playback location where a head mechanism is located. In a stationary head tape drive, the head mechanism consists of a plurality of heads which are transversely aligned and fixedly positioned with respect to the tape during record and playback. Information is placed on the tape in the form of a plurality of parallel, longitudinally-extending tracks; the areal density of information stored on the tape is increased by reducing the dimensions of the heads and the inter-head spacing on the head mechanism. However, small head size and minimal inter-head spacing demand great precision in the manufacture of head components. As a result, the manufacturing tolerances of the tape drive, primarily the mechanical tolerances of the head assemblies, have become increasingly stringent and more difficult and expensive to achieve. Further, the proliferation of heads is reflected in additional read and write channel electronics for each head which also adds to the expense of these drives.
As is known, in the video recording art, modem high-capacity, high-quality tape drives employ head mechanisms which rotate magnetic heads with respect to a moving tape. The high rotational speed of the "rotary head" recorders steps away from the requirement in stationary head technology for a plurality of transversely-aligned heads and associated electronics and, therefore, obviates the problems attendant with manufacture and assembly of stationary head mechanisms. Servoing is employed in the dominant classes of rotary head tape drives to align rotating heads with tracks on the tape. The servoing techniques developed for these classes of tape drives enhance head/track alignment and result in substantial reduction in track width and inter-track spacing. Consequently, rotary head tape drives enjoy a significant advantage over stationary head tape drives in areal density.
One type of rotary head drive is an arcuately scanning tape drive which employs a circular head assembly. In this head assembly a plurality of read and write magnetic heads are mounted on a front end of a cylindrical dram in substantially a circle about a center of the drum. During operation, the drum rotates and the tape moves across the front end in contact with the heads. The result is a sequence of arcuately-shaped tracks on the tape which are transverse to the longitudinal axis of the tape. Prior art arcuately scanning tape drives are described, for example, in: U.S. Pat. No. 2,750,449 of Thompson, et al.; U.S. Pat. No. 2,924,668 of Hoshino, et al.; U.S. Pat. No. 3,320,371 of Bach; U.S. Pat. No. 4,636,886 of Schwarz; U.S. Pat. No. 4,647,993 of Schwarz, et al; and U.S. Pat. No. 4,731,681 of Ogata.
In an arcuately scanning tape drive, a magnetic head commences a write or read function at edge of the tape and continues to write or read until it leaves the opposite edge of the tape. During this write or read function it is imperative that good transducing contact be maintained between the head and the tape as the head arcs across the width of the tape. Any region of the tape where there is inadequate contact is a deadband region which produces signal loss during recording or playback.
Arcuately scanning tape drives typically have inadequate contact near the edges of the magnetic tape. This results from a low tensile-stress field at the tape edges because the tape is wrapping around an annular edge. As a consequence, the center of the tape has higher tension than the edges and head/tape contact is adequate in the center becoming less as the head moves out to the tape edges. The same thing occurs with a magnetic tape. When the head assembly of an arcuate scanner is forced against a magnetic tape to implement the read and write functions there is not enough edge tension to maintain the desired contact. Resultantly, the magnetic tape has top and bottom deadband regions which effectively reduce the usable width of the tape. This condition seriously affects the efficiency of the arcuately scanning tape drive.